A wide angle and a high resolution are required in a lens which has been recently used in a monitoring application or in an on-vehicle application. In the wide-angle lens, the magnification chromatic aberration is required to be corrected for obtaining a high resolution and thus a wide-angle lens is constituted by combining a plurality of lenses to correct the magnification chromatic aberration. For example, as shown in FIG. 8, a wide-angle lens has been proposed which is constituted of five lenses in four groups and whose viewing angle is widened (see Japanese Patent Laid-Open No. 2009-63877).
The wide-angle lens shown in FIG. 8 comprises, in order from an object side (object to be photographed side/front side), a first lens group 11 having negative power, a second lens group 12 having negative power, a third lens group 13 having positive power and a fourth lens group 14 having positive power. A diaphragm 91 is provided between the third lens group 13 and the fourth lens group 14. In this embodiment, an infrared filter 92 is disposed on a rear side (image side/opposite side to object side) with respect to the fourth lens group 14. The first lens group 11 is made of a glass lens 81 having negative power and the lens 81 is a spherical lens whose object side face and image side face are a spherical surface. The second lens group 12 is made of a plastic lens 82 having negative power and both faces of the plastic lens 82 are an aspherical surface. The third lens group 13 is made of a plastic lens 83 having positive power and both faces of the plastic lens 83 are an aspherical surface. The fourth lens group 14 is constituted of a cemented lens made of a plastic lens 84 having negative power and a plastic lens 85 having positive power and respective both faces of the plastic lenses 84 and 85 are an aspherical surface.
However, even if the resolution is tried to be further enhanced while attaining a low cost of the wide-angle lens, the magnification chromatic aberration of the wide-angle lens constituted as shown in FIG. 8 is unable to be corrected sufficiently. More specifically, as understood from the defocus MTF (Modulation Transfer Function) characteristics of the wide-angle lens shown in FIG. 9(a) and the spot diagram of the wide-angle lens shown in FIG. 9(b), a high resolution corresponding to 2M pixels or the like cannot be obtained. In FIG. 9(a), the solid line “L91” indicates an OTF (Optical Transfer Function) coefficient at a center part of the lens, the dotted line “L92” indicates an OTF coefficient in a radial direction of a peripheral part of the lens, and the alternate long and short dash line “L93” indicates an OTF coefficient in a concentric direction of the peripheral part of the lens. Further, light condensed states of red light, green light and blue light are collectively shown in FIG. 9(b).